In situ combustion process



April30,1963

INJECTION WELL TAIR FUEL F OIL 8 GAS COMBUSTION OF EXCESS SHALEOVERBURDEN OXYGEN WITH INJECTED W FUEL in I OVERBURN 7" @W a I Max-COKESI RESIDUAL/O1.

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Eugene R. Elzingu Inventor U UJW Patent Afrorney United States Patent3,087,541 IN SITU COMBUSTION PROCESS Eugene R. Elzinga, Scotch Plains,N.J., assignor to Jersey Production Research Company, a corporation ofDelaware Filed May 9, 1960, Ser. No. 27,666 3 Claims. (Cl. 166-11) Thepresent invention is concerned with thermal methods for the recovery ofpetroleum from subterranean reservoirs. The invention is moreparticularly related to a. unique technique for recovering oil frompartially depleted reservoirs by the in situ combustion. of some of thecarbonaceous materials present in such reservoirs. The inventionespecially relates to an improved in situ combustion process wherein themaximum utilization of oxygen is secured and breakthrough of the oxygento the production well with resultant corrosiveness is prevented. Inessence the operation comprises a two-stage technique wherein in thesecond stage fuel and the oxygen are so injected so as to securecombustion in the area previously burnt out in the initial stage.

In the recovery of oil from subterranean reservoirs, there have beensubstantial advances in primary recovery techniques so as tosubstantially increase the recovery of oil. However, an appreciablequantity of the oil remains in the reservoir after termination of theprimary recovery methods. It is estimated that only about 30 to 50% ofthe oil can be economically recovered by primary recovery techniques. Agreater amount may be recovered by other secondary techniques, such asre-pres-suring treatments following the primary method.

Thus, there exists a great interest in secondary recovery methods.Secondary recovery is the recovery of additional quantities of oil froma reservoir after it is no longer economical to recover oil by primaryrecovery methods. 'For example, a secondary operation may be conductedby drilling one or more injection wells into a permeable oil bearingformation within suitable proximity to a producing well or wells whichare drilled into this same permeable oil bearing formation. Injection ofliquids or gases through the injection well is generally effective inincreasing the oil production from the producing well or wells. Thistechnique of secondary recovery enables the recovery of substantiallymore oil than can be produced by primary recovery methods.

As pointed out, the use of a number of secondary recovery procedures forremoving oil from subterranean oil reservoirs are well known in thepetroleum industry. It is the function of such procedures to makepossible the recovery of oil from reservoirs after primary productionmethods are uneconomical. In general, all secondary recovery proceduresemploy a driving medium such as a liquid or gas for displacingadditional oil from a reservoir,

Other desirable methods for recovering oilfrompartially depletedunderground reservoirs comprise in situ combustion methods. Thesemethods in essence involve the establishment of a combustion frontwithin the reservoir in the vicinity of one or more injection wells andthe subsequent introduction of a combustion-supporting gas behind thecombustion front in order to move the combustion front through thereservoir toward one or more production wells. As the combustion frontadvances, the heat liberated results in the vaporization of oil from ahigh temperature zone preceding the front. Cracking and the formation ofcoke which serves as fuel for the process also occur. The resulting oilvapors are carried forward with the combustion products and condensed incooler portions of the reservoir. Heat transfer to cold oil in sectionsof the reservoir in front of the advancing high temperature zone leadsto a reduction in viscosity of the oil and facilitates its displacementfrom the reservoir. A

mixture of oil and gases is withdrawn from the reservoir at theproduction well and. the oil contained therein is subsequentlyrecovered.

Although these processes known in the art are promising, there existsome difiiculties associated with them. One disadvantage is that thecombustion front and the associated high temperature zone finger throughhigh permeability sections of the reservoir instead of advancinguniformly. This leads to breakthrough of the combustion front into theproduction Well as an early stage in the process when only a small areaof the reservoir has been been burnt through. After such a breakthroughoccurs, the high temperature combustion products, the oxygen and the oilflow into the production well simultaneously, creating a danger of firein the wellbore and in the associated equipment. Furthermore severecorrosion of the equipment in the producing well or wells occurs.

Difiiculties of the type described above are encountered in bothStratified and unstratified reservoirs. In stratified reservoirs, someof the strata frequently have much greater permeability than others.Breakthrough of the combustion front at the producing well through ahigh permeability stratus results in a direct channel through which theinjected oxygen may pass from the injection well to the production wellwithout encountering significant quantities of unburned hydrocarbons.Recovery from the adjacent strata of relatively low permeability is slowand must be carried out in the face of undesirably high temperatures andfree oxygen in the production well.

In unstratified reservoirs, breakthrough generally occurs at'theproduction Well near the top of the producing formation due tooverburning. Utilization of the injected oxygen thereafter dependsprimarily upon the diffusion of gaseous oxygen from the burned out areaat the top of the reservoir down into the unburned zone. The distancethrough which the oxygen must diffuse increases as the thickness of theburned-out zone increases and hence the portion of the injected oxygenutilized to support combustion is apt to decline as the operationprogresses. The result is a continual increase in the difficultiesoccasioned by the presence of free oxygen in the production well.

Summarizing increased crude production is achieved in the undergroundburning process due to heat released when air is injected underground toburn part of the crude in place. The efficiency of the process dependsupon how much air is required to produce a barrel of oil which in turnis tied to how much injected oxygen is consumed by combustion.Unfortunately, laboratory and field experiments have shown that for asubstantial part of the process, 60% or more of the injected oxygen isnot consumed or is consumed in the producing well. The present inventionis concerned with a method for increasing oxygen utilization in thereservoir where it will do the most good and in addition will cut downon corrosion problems in the producing well.

As mentioned heretofore one reason for low oxygen utilization is thatinjected air fingers through the top of the reservoir between injectionand producing wells. After the residual oil in this finger is consumedthe air flowing through this region no longer comes into direct contactwith oil and hence only that portion of its oxygen which can diffusedown to the combustion front is utilized. Since a large portion of theinjected air flows through this burned-out region, because of its lowerresistance to flow, large quantities (60%) of oxygen bypasses thecombustion zone. Under these circumstances, combustion can take place inonly two regionsthe first region is by direct contact of oxygen with oilin the reservoir and the second region is in the producing well. Thecombustion in the reservoir produces heat which is utilized in theprocess. On the other hand, combustion in the producing well is bad fortwo reasons: first heat released at the producing well is not effectivein reducing oil viscosity in the bulk of the reservoir. Secondly, as aconsequence of the concentrated heat released at the producing well,temperatures increase to a point where corrosion becomes a seriousproblem.

In accordance with the present invention these harmful effects areeliminated by a technique wherein all the injected oxygen is consumedbefore the oxygen reaches the producing well. This is accomplished bythe injection of either liquid or gaseous hydrocarbons from theinjection well into the overburnt section in a manner to react the thickhydrocarbons with oxygen which is also injected into the overburntsection or region. It is important that the fuel is not mixed with theinjected air until after the fuel has flowed away from the injectionwell, otherwise a situation will exist similar to that previouslydescribed with respect to in situ combustion. This nonmixing of thehydrocarbon and oxygen is accomplished by injecting the fuel near thetop of the formation while the air is injected near the bottom of theoil sand. Thus, suflicient oxygen for combustion is not encountereduntil the fuel has traveled well out into the reservoir. Even if somecombustion should occur near the injection well, serious corrosion willnot occur since the corrosive products of combustion do not flow intothe injection well.

A typical operation, for example, will proceed in the following manner.Air is injected into the reservoir in order to establish igaspermeability of the formation between the injection well or wells andthe producing well or wells. Combustion is then initiated in anysatisfactory manner such as by heaters, by chemical methods, or byspontaneous ignition. The process is then continued in a conventionalmanner until an overburn region has been established and until oxygen isproduced at the producing well. In a second phase or stage liquid orgaseous fuel is injected near the top of the formation in order to reactwith the oxygen flowing through the overburnt region which oxygen isintroduced at a lower point, preferably near the bottom of theoil-bearing sand. The fuel injection rate as well as the oxygeninjection rate is controlled in order to give little or no oxygen in theproduced gases from the production well.

By the present invention, more heat is liberated in the right place/unit of injected air. Therefore, more oil will be produced with thisair. Secondly, the producing well temperatures will be lower, therebyreducing and minimizing corrosion. The fuel introduced at the injectionwell may comprise produced hydrocarbon gases or produce crude from theproduction well.

The present invention may be fully understood by referring to thedrawing illustrating one adaptation of the same.

Referring now to the figure, reference numeral 11 designates aninjection well drilled through overburden 2 into an oil-bearingreservoir 3. Production well 4 has been drilled into the reservoir at apoint removed from the injection well. \In accordance with the presentinvention, packer elements 5 and 6 are positioned in the annular areabetween the drill string 7 and the bore hole wall. These packer elementsmay be adjusted along the pipe string either upwardly or downwardly soas to positively control the point of injection of the fuel and of theoxygen containing gas. The distance separating the injection andproduction wells will depend upon a number of factors, including theextent of the reservoir, the permeability and porosity of the subsurfacestrata, the reservoir pressure, and the recovery pattern utilized. Thisdistance may vary widely but will generally range between about 300 feetand about 3,000 feet. The injection and production wells will normallybe cased and perforated opposite the pro ducing strata in theconventional manner but in some instances uncased wells may be used.Conventional facilities for introducing air and other gases at theinjection well and for recovering and separating oil and gaseousproducts from the production well are provided on the surface.

-In the first phase of the present invention in situ combustion iscarried out in the reservoir by establishing a combustion front in thevicinity of the injection well and thereafter injecting air in order topropel the front through the reservoir toward the production well. Anumber of methods for establishing such a front are well known,including the injection of high temperature combustion products into thereservoir, the use of electrical devices to ignite a mixture of fuel gasand oxygen in the injection well opposite the producing formation, andthe injection of pyrophoric materials and a stream ofcombustion-supporting gas into the reservoir through the injection well.As shown in the drawing, overburning occurs in area 8 as the combustionfront thus established progressed through the reservoir. The upperportion 8 of the reservoir was substantially burned out and thusdepleted of oil. The lower section 9 of the reservoir, on the otherhand, was relatively unaffected by passage of the combustion front andhence still contains appreciable quantities of oil. Reference numeral 10designates the boundary between the burned and unburned sections. DottedLine 11 indicates the additional depth to which it can be expectedburning will occur in the reservoir by the present technique.Breakthrough of the combustion front in the initial phase occurred inthe production Well near the top of the producing zone. As a result ofthe overburning and premature breakthrough of the combustion front,continued injection of air or oxygen by conventional methods into thereservoir would result in combustion near or in the production well. Asubstantial portion of the injected oxygen thus would flow through thehigh permeability burned-out Zone at the top of the reservoir and wouldbe lost for the generation of heat within the reservoir. in situcombustion in the section of the reservoir below the burned-out zonedepends largely upon the diffusion of oxygen downardly into the coolerregion at the bottom of the reservoir. Since this occurs only to alimited extent, utilization of oxygen and overall efiiciency of theprocess would be poor.

In carrying out the process of the present invention, the conventionalinjection of air or oxygen at injection well 1 is discontinued uponbreakthrough of the combustion front at production well 4. Imminentbreakthrough of the combustion front can often be detected by observingthe production well temperature. A substantial rise in temperature over.a relatively short period of time generally indicates that combustionis occurring in the area immediately surrounding the production well.The appearance of oxygen in the product gases indicates thatbreakthrough has occurred.

At this point the first phase is finished and combustion is carried outin the following manner. A combustible gas or liquid is introduced intothe top of the formation above packer 5 through the annular area betweenthe pipe string 7 and the bore hole Wall. An oxygen containing gas isintroduced downwardly within the pipe string and is forced into theformation below packer element 6. In this manner combustion will occurin the burnt out area 8, particularly in subsection 12. The amount offuel and oxygen introduced is so controlled that substantially nocombustion occurs at the production well. By this technique the burntout area 8 is maintained continuously with a relatively hightemperature, which temperature will diffuse downwardly into area 9 andwill thus cause oil to flow from the oil-bearing sand into producingwell 4.

The pressures at which the gases are introduced may range from valuesslightly in excess of the formation pressures up to values approachingpressures at which fracturing of the reservoir occurs. Pressures betweenabout p.s.i.g. and about 1,000 p.s.i.g. are generally preferred. Heatliberated due to combustion of the fuel gas is carried toward theproduction well by conduction of the hot gases. The temperature of theportion of the reservoir down stream from the combustion front throughwhich the gases flow rises. Over-lying and underlying portions of thereservoir are heated by conduction. As heat diffuses into theoil-saturated rock below the burned zone, the viscosity of the oil isreduced. The oil moves toward the producing well by the imposed pressuregradient between the well-s and by the hydrostatic pressur'e of the oil.

While the invention has been particularly described in conjunction witha secondary recovery operation, it is to be understood that thetechnique may be also utilized in primary operations, particularly, inproducing heavy crudes. In essence, the operation is concerned with anin-situ technique wherein oxygen does not reach the production well,thereby materially reducing corrosion and greatly increasing theproduction of oil.

What is claimed is:

1. An in situ combustion process for the production of oil from an oilbearing subterranean reservoir penetrated by an injection well and aproduction well, said reservoir being characterized by a tendency tooverburn, which comprises injecting an oxygen-containing gas into saidreservoir through said injection well, igniting said reservoir oil inthe vicinity of said injection well thereby generating a combustionfront; propagating said combustion front toward said production well bycontinuing said injection of oxygen-containing gas; producing oil fromsaid production well; continuing to inject oxygencontaining gas untilsaid combustion front reaches the the burned region of said reservoirthrough which said combustion front has passed, said step of introducingfuel being commenced before the temperature of said burned region 'hasfallen below the ignition temperature of said fuel; concurrently andseparately introducing additional quantities of oxygen-containing gasinto said burned region of said reservoir, whereby combustion of saidintroduced fuel is achieved in said burned region simultaneously withthe continued combustion of reservoir hydrocarbons; continuing saidconcurrent and separate injection of iiuel and oxygen-containing gas insaid burned region, whereby continued combustion in said burned regioncauses a heat front to move downwardly within said reservoir, therebyforcing additional quantities of oil toward said production well;controlling the rate of injection of said fuel in order to provide asubstantial absence of oxygen in the gases produced from the productionwell; and producing additional quantities of oil from said productionwell.

2. Process as defined by claim 1 wherein Said introduced fuel comprisesa fuel produced from said production well.

3. Process :as defined by claim 1 wherein said fuel is introduced intothe upper area of said reservoir and wherein said additional quantitiesof oxygen-containing gas are introduced into the lower area of saidreservoir.

Simm et a1. May 28, 1957 Crawzfiord Nov. "17, 1959

1. AN IN SITU COMBUSTION PROCESS FOR THE PRODUCTION OF OIL FROM ANOIL-BEARING SUBTERRANEAN RESERVOIR PENETRATED BY AN INJECTION WELL ANDPRODUCTION WELL, SAID RESERVOIR BEING CHARACTERIZED BY A TENDENCY TOOVERBURN, WHICH COMPRISES INJECTING AN OXYGEN-CONTAINING GAS INTO SAIDRESERVOIR THROUGH SAID INJECTION WELL, IGNITING SAID RESERVOIR OIL INTHE VICINITY OF SAID INJECTION WELL THEREBY GENERATING A COMBUSTIONFRONT; PROPAGATING SAID COMBUSTION FRONT TOWARD SAID PRODUCTION WELL BYCONTINUING SAID INJECTION OF OXYGEN-CONTAINING GAS; PRODUCING OIL FROMSAID PRODUCTION WELL; CONTINUING TO INJECT OXYGENCONTAINING GAS UNTILSAID COMBUSTION FRONT REACHES THE VICINITY OF SAID PRODUCTION WELL;THEREAFTER, WHILE COMBUSTION OF RESERVOIR OIL CONTINUES, INTRODUCING AFUEL INTO THE BURNED REGION OF SAID RESERVOIR THROUGH WHICH SAIDCOMBUSTION FRONT HAS PASSED, SAID STEP OF INTRODUCING FUEL BBEINGCOMMENCED BEFORE THE TEMPERATURE OF SAID BURNED REGION HAS FALLEN BELOWTHE IGNITION TEMPERATURE OF SAID FUEL; CONCURRENTLY AND SEPARATELYINTRODUCING ADDITIONAL